A chemical aqueous phase radical mechanism for tropospheric chemistry

Chemosphere, Vol. 38, No. 6, pp. 1223-1232, 1999

Pergamon

© 1999 Elsevier Science Ltd. All rights reserved 0045-6535/99/$ - see front matter

PII: S0045-6535 (98)00520-7 A CHEMICAL AQUEOUS PHASE RADICAL MECHANISM

FOR TROPOSPHERIC CHEMISTRY H. Herrmann a/,, B. Ervens a), p. Nowacki a), R. Wolke a) and R. Zellner b)

a) Institut ftir Troposph~irenforschung, Permoserstr. 15, 04303 Leipzig, Germany b~Institut ftir Physikalische und Theoretische Chemie, FB 8, Universit~t GH Essen, Universit!itsstr. 5, 45117 Essen, Germany

Abstract In the present work model simulations with a box model applying typical tropospheric initial conditions for three different scenarios (marine, rural and urban conditions) are performed to model tropospheric chemistry in both the gas and the aqueous phase. The gas phase chemistry is described by RADM2 [1]. For the aqueous phase chemistry a detailed aqueous phase mechanism (CAPRAM, chemical _aqueous phase radical mechanism) was developed. This mechanism is more extensive than other existing mechanisms, because the oxidation of organic compounds with one and two carbon atoms, an explicit description of radical or iron(llI) initiated S(IV)-oxidation, the reactions of radicals and radical anions .OH, NOy,.CI2, .Br2-, and CO3-., and the chemistry of the dissolved transition metal ions (TMI) iron, manganese and copper is treated in detail.

1 Introduction Several studies in recent years [2 - 5] have shown the influence of aqueous phase processes on tropospheric chemistry. In most developed aqueous phase mechanisms mostly organic species with only one carbon atom are considered, In CAPRAM organic compounds with two carbon atoms are also included. Starting from the alcohols, methanol and ethanol, the aldehydes and acids are produced. Each oxidation step may be initiated by radicals or radical anions such as .OH, NO3., SOn-., .C12, .Br2- or CO3-.. Such radicals and radical anions may be important species for the description of chemical transformation of tropospheric constituents in the aqueous phase. Not only the primary radicals -OH and NO3- which may be transferred from the gas phase into the liquid phase, but also the secondary radical anions SO4-., .C12, .Br2- and CO3-. may initiate a wide variety of processes. The chemical aqueous phase radical mechanism presented here includes an elaborated reaction scheme with production and destruction reactions for the radical anions. Moreover, the reaction rates for the mechanism are updated using existing kinetic data, which are critically revised. In recent studies [6 - 8] it was shown, that in the marine scenario the importance of chemistry of halogen atoms is comparable to that of the OH radical. Therefore an extension of the basis mechanism CAPRAM were elaborated. This additional mechanism of halogen activation is based on the mechanism by Sander and Crutzen [8], but it was extended by several equilibria and reactions. 1223

1224 2 The box model A simple box model without emission, deposition, horizontal and vertical transport is used for the simulations. The meteorological parameters, such as the temperature and pressure, are constant during the three days of simulation (T = 288.15 K, p = 1 atm). A liquid water content of 0.3 g m -3 is assumed. The gas phase chemistry is currently described by RADM2 [1]. Besides the species CH3OH, C2HsOH, C12 and Br2 are additionally treated. The aqueous phase chemistry is represented by CAPRAM (Chemical Aqueous Phase Radical Mechanism). This mechanism contains 208 aqueous phase reactions and 26 equilibria. In total 34 heterogeneous processes are included. The phase transfer from the gas phase and vice versa is treated by means of the resistance model by Schwartz [9]. Hence, apart from Henry constants also the mass accommodation coefficients and the gas phase diffusion coefficients are implemented (Table 2). In existing aqueous phase mechanisms [2 - 5] the organic chemistry is restricted to Ci species. CAPRAM represents a mechanism, in which also reactions with C~ species are included. Furthermore, CAPRAM contains various radical reactions of .C12, .Br2-, SO4 -., CO3-.. Also reactions with peroxy radicals, such as the methy!peroxy radical, the acetylperoxy radical (ACO3) and others are considered in the aqueous phase. The used mechanism is applied for all three scenarios. In additional calculations a radical-driven halogen activation under marine conditions was considered. For this a additional mechanism was formulated including reactions between halogen containing species in the aqueous phase also the uptake processes of HOCI, HOBr and BrCI and the photolysis processes of these species as well as C12 and Br2 in the gas phase. Test calculations have shown that the efficiency of the photolysis processes of these species in the aqueous phase were very small, so that these reactions were not included in the mechanism. In the gas phase the reactions of the bromine and chlorine atom with ozone and methane and the reactions of BrO. and C10. with ozone and HO2. were added. Due to space limitations the references of all parameters and reaction rates will be published in more detail elsewhere [10]. Table 1: Initial concentrations for three scenarios under urban, remote and marine conditions, gasphase species in ppb, aqueous phase species in m o l / l ( M ) Species

urban

remote

marine

NO~

4.5

1.5

3.10 4

HNO3

1

03 SO2 HCI NH~

9(1 10 6 25 5 105

0.3 6(1

0.15 40 0.1 0.5 0.05 3.3. 105

1

CH4 NMOC CH3OH ETOH

1700

1

0.7 15 3.3.10 ~ 1700 4.(1 2 0.24

O2(aq)

3 , 10 .4

3.10 `4

3 • 104

pH

CI Br

4.5 1. 10 4

4.5 I . 10 4

5.2 5.6. 10 .4

3 • 10 6

3 . 10 .7

Fe 3+

5 . |0 6

5.10 7

1.8. 10-6 5 . 10-8

M n 3+

2.5- 10 7 2,5. 10 7 5.97.10 -6 3 . 10 .5

2.5. 10-8

1. 10 9

2.5. 10-8 5,97.10 `6 3 . 10 5

1 . 10-9 5.97,10 .7 3 . 10 -6

CO:

Cu + HSO4

5042

6.8 5

1700 2.4 0.8 2.4, 10 3

1225

Table 2: CAPRAM: Uptake Parameters Reaction No. HI H2 H3 H4 H5 H6 H7 H8 H9 H I0 H 11 H 12 H 13 H14 H 15 H 16 H 17 H 18 H19 H20 H21 H22 H23 H24 H25 H26 H27 H28 H29 H30 H31 H32 H33 H34

Species CO2 HCI NH3 03 HO2 OH H202 HNO3 NO3 N205 NO2 HNO2 HO2NO2 SO2 HCHO~ CH3OOH CH3C(O)OOH CH3OH C2HsOH CH3CHO b HCOOH CH3COOH CH302 ETHI~ C12 Br2 H2SO4 CH4 C2H6 C2H 4

Kr129S, M arma 3.11 • 10.2 1.10 60.7 1.14. 10 .2 9 . lO~ 25 1.02. 105 2.1 . 105

0.6 1.4 1.2. 10.2 49 1 . 105d 1.24

3.0. 103 6 6.69. 102 2.2. 102 1.9. 102 11.4

5 . 5 3 . 103 5 . 5 0 . 103 6 6d 9 . 1 5 . 10.2 0.758 2.1.1o 5 1.46.10 .3 1 . 9 5 . 1 0 .3 4.55.10 .3

PANIc OP2 f OL2P g ACO3 h

AH29s, kJ mol -j -20.14 -16.8 -32.6 -19.l -43.9 -52.7 -72.3

-10.5 -40.6 -27 -60 -44.2 -49.0 -44.8 -52.3 -52 -46.8 -49.0 -46.9 -46.9 d 20.7 31.6

5 837 6 669 a Equilibrium H C H O (g) ~ CH2(OH)2 (aq).; b Equilibrium c Peroxy radical with 2 carbon atoms.; d Estimated value.; • oxides; z Peroxy radicals of C2H4; h Acetyl peroxy radical

Dg [105 m 2 s_l]

tx

2.10 .4 1.55 0.064 1.89 0.04 2.3 5 . 1 0 .2 1.48 0.01 1.04 0.05 1.53 0.11 1.46 0.054 1.32 4.10 3 1.00 3.7-10-3 1.10 1.5.10-3 1.92 0.5 1.30 0.1 1.30 3 . 5 . 1 0 .2 1.28 0.02 1.64 3.8.10 .3 1.31 0.019 1.02 1.5. 10 .2 1.16 8.2.10 .3 0.95 0.03 1.22 0.012 1.53 0.019 1.24 3.8-10-3 1.35 8.2. 10 3 1.08 0.03 1.28 0.03 1.00 0.07 1.30 5-10.5 1.41 1 . 10-4 0.95 1 • 10.4 1.01 0.019 0.63 0.01 0.76 8.2.10 .3 0.82 0.019 1.0 CH3CHO (g) ~ CH3CH(OH)2 (aq).; Peroxy acetyl nitrate f C2-hydroper-

Table 3. CAPRAM: Aqueous equilibria Reaction No. El E2 E3 E4 E5 E6 E7 E8 E9 El0 Ell El2 El3 El4 El5 El6

k f.ZgSK. Reactions H20

°

~ I--I + + OH

CO2+H20 ~ H2CO3 H2CO3 7 " - " I-I++ HCO3 HCO3- ~ H++CO32HCI ~ I-I+ + CINH3 + H20 ~ NH4+ + OHHO2 ~ H*+O2" HNO3 ~ H++NOs HNO2 ~ H + + NO2 HO2NO2 ~ H* + O2NO2NO2 + HO2 ~ HO2NO2 SO2+H20 ~ HSO3-+ H + HSO3" ~ "'" SO32"+ I-I+ HSO4- ~ SO42" + H + HCOOH ~ HCOO" + I-l+ HAc ~ A c ' + IF"

M * sa

E,/R. K

kb. 29~. M " sl

2.34. I0 -s

6800

1.3 • I0 I~

4.3.10 .2 1. 107 2.35 8.6. 1 0 1 6 6.02. 105 8.0. 105 1.1 . 1 0 1 2 2.65 . 107 5 . 105 1.0. 107 6.27.104 3110 1.02" 109 8.85 • 106 8.75.105

9250

5.6.104 5 . 1 0 I° 5 . 10 j° 5 . 10 j° 3.4 • 10 j° 5 . 10 I° 5 . 1 0 l° 5 • 10 ~° 5 . 101° 4.6- 10.3 2.0.10 s 5.101° 1 ' 1011 5 - 10 l° 5 . 10 l°

1820 -6890 560 0 -1800 1760

-1940 -1960 -2700 -12 -46

E,/R. K

8500

0

1226 El7

Fe 3+ + H 2 0 ~

El8

[Fe(OH)]Z++ H 2 0 ~

El9

Fe3++SO42

E20

HCHO+H20

[Fe(OH)] 2+ + H + ~ ~

E21a

CH3CHO + H20 ~

E21b E22

CH2(OH)2 + H S O f ~ CHz(OH)2 + SO~ 2 ~

E23 E24 E25 E26 E27 E28 E29 E30

CI+CI

4.7 • 104

4.3 • 10 s

[Fe(OH)2]+ + H +

1.1 • 103

8.0. 109

[Fe(SO4)I +

3.2.103

CH~(OH)2

0.18

-4030

5 . 1 . IO3

1.4. 10 .4

-2500

5.69. 10-

790 2.5. 107

2990 2450

790 3.95 • l i f e

CH3CH(OH)2

~

HMS + H20 H M S + OHC12

Br+ Br ~ CI + O H ~ CIOH + H ÷ ~ C I O H + CI ~ Br + O H ~ BrOH + H ÷ ~ BrOH + Br ~

1.8.105

2 . 7 " 1 0 It

1.4.105

1.2. 10 u 4.3.109 2.1"10 m 1.0.104 1.1.10 m 4.4.10 I° 1.9.108

1.9. 104 6.1.109 1.3.103 4.5.107 3.3.107 2.45.10 .2 2.7.106

Br2 CIOH C1 + H 2 0 C12 + OHBrOH Br + H 2 0 B r z + OH-

2990 5530

HMS-: H 2 C ( O H ) S O f , H A c : C H 3 C O O H , A c : C H 3 C O O ; b Estimated value. Tabl......_L_e: C A P R A M : Ac aeous-Phase reaction rate constants Reaction Reacti°n~ No,

k298,

M" s l

E, / R, K

HOx- and TMl-Chemistry R1

H202 + Fe 3. "-+ HO2 + H + + Fe 2+

6 . 0 . 102

R2

H202 + [Fe(OH)] 2÷ --') HO2 + H 2 0 + Fe 2+

6.0- 102

R3

H202 + [Fe(OH)2] + --+ HOz + O H + Fe 2÷ + H 2 0 H202 + Fe 2+ --+ O H + O H + Fe 3+

6 . 0 . 102

R4 R5 R6

H202 + Mn 3+ --9 HO2 + H + + Mn 2+

76 7 . 3 , 104 7,0 . 103

R7

H202 + Cu + --') O H + OH" + Cu 2+ O f + Fe 3÷ ---) 02 + Fe z+

R8

H 0 2 + [Fe(OH)] 2+ --) Fe 2+ + 02 + H 2 0

1,3 • 105

R9

O2 + [Fe(OH)] 2+ --4 O2 + Fe 2. + O H

1,5 • 108

RI0

O f + [Fe(OH)2] ÷ --~ 02 + Fe 2+ + 2 O H

Rll

0 2 + Fe 2+

RI2

HO2 + Fe 2+

RI3

02 + M n 2+

R15

H O 2 + M n 2+

RI7 R18

w ) H202 + Fe 3+

O H + Fe 2+ ~ [Fe(OH)] 2+

RI4

RI6

2FV ) H202 + Fe 3+

2H+ ) H2Oz+Mn3+ H* ) H 2 0 2 + M n 3+

O H + Mn 2+ -.,', O H + Mn 3+ 02 + Cu +

2H* ) H202 + Cu 2+

1.5

. 10 s

1,5 • lO s 1,0. 107 1,2 • 106

5050

4,3 • lO s

1100

1.1. 108 2.105 2.6 • 107 9 . 4 . 109 2 . 2 . 109

R19

HO2 + CH ÷ H' ) H202 + CU 2+ O H + Cu + -+ O H + Cu 2÷

R20

H O 2 + Cu 2+ ___)02 + Cu + + H +

1.2. 109

R21

0 2 + Cu 2. --~ 02 + Cu + Fe 3+ + Cu ÷ --) Fe z+ + Cu 2+

1.1. 10 I°

[Fe(OH)] 2+ + Cu ÷ ---) Fe 2+ + Cu 2÷ + OH-

3 . 107

R22 R23 R24 R25 R26 R27 R28 R29 R30 R31

[Fe(OH)2] ÷ + Cu + --0 Fe 2÷ + Cu 2÷ + 2 0 H Fe 2. + M n 3+ _+ Fe 3. + Mn 2* H÷ 03+02 ) 2 O2 + O H HO2 + HO2 - + 02 + H202 H÷ HO2 + O 2 ) H202 + 02 HO2 + O H ~ H 2 0 + 02 02- + O H --~ O H + 02 H202 + O H ~ H O 2 + H 2 0

R32 R33 R34

M H P + O H ---) CH302 + H 2 0 H S O 3 + O H --0 H 2 0 + S O 3 SO32 + O H ---4 O H + S O 3

R35 R36

N205 + H 2 0 --q' 2 H + + 2 N O 3 NO3 + O H --4 N O 3 + O H

3 . 109

3 . 107 3 , 107

1.5.104 1.5.109 8.3. 105 9 . 7 . 107 1.0 • 10 t° IA - 101° 3.0 • 107 3 . 0 ' 10 TM 2 . 7 . 109 4 . 6 . 109

2720 1060

2120 1680 1680 b

N-Chemistry 5"109

1800

9 . 4 ' 107

2700

1227

R37 R38 R39 R40 R41 R42 R43 R44 R45 R46 R47 R48 R49

NO3 + Fe 2+ ~ NO3" + Fe 3+ NO3 + Mn 2÷ ---) NO3- + Mn 3÷

8 • 106

1.1 • 106 4 . 9 . 106 4 . 9 . 106b

NO3 + H2Oz ---) NO3 + H + + HO2 NO3 + MHP --~ NO3 + H+ + CH302 NO3 + HO2 --> NO3- + H + + 0 2 NO3 + O2 --4 NO3- + O: NO3 + HSO3- ~ N O r + H + + SO3NO3 + SO32" --) NO3- + SO3NO3 + HSO4- ~ NO3" + H + + SO4N O 3 + SO42° ~ NO3" + S O a NO2 + O H --~ NO3- + H + NO2 + 02" "-~ NO2- + 02 NO2 + NO2

R50 R51 R52 R53 R54 R55 R56 R57 R58

2000 2000 b

3.o. 1o9

3 " 109b 1.3. 109 3.0- 108 5 . 6 . 103 2.5.104 1.2. 10 l° 1. l 0 s 1 - l0 s

H20 ) HNO2 + NO3" + H +

2000

-2900

4 . 5 . I0-2

O2NO2- "-'¢NO2- + 02 NO2 + OH -'~ NO2 + O H N O r + SO4 "-'* SO42- + NO2 NO2- + NO3 -'> NO3- + NO2 NO2 + 0 2 - --) 2 CI" + NO2 NO2- + Br2- --) 2 Br" + NO2 NO2- + CO3- ~ CO32- + NO2 NO2 + 03 --->NO3" + 02 HNO2+ OH ---) NO2+ H 2 0

1.1 • 1 0 I°

7.2. 108 1.4. 109 6 . 107 1.2. 107 6 . 6 . 105 5 . 105 1 • 109

1720 850 6900

S-Chemistry R59 R60 R61 R62 R63 R64 R65 R66 R67 R68 R69 RT0 R71 R72 R73 R74 R75 R76 R77 R78 R79 R80 R81 R82 R83 R84 R85 R86 R87 R88 R89 R90 R91 R92 R93 R94

HMS- + OH

O2/H20 ) H 2 0 + H O 2 + H C O O H

H M S " + SO4- --~ SO42- + H + + H C H O HMS" + NO3 ~ NOr + H + + HCHO H M S " + 0 2 --~ 2 CI" + H + + H C H O H M S " + Br2- ~ 2 Br- + H + + H C H O HSO3" + H202 + H + ~ SO42" + H z O HSO3- + M H P

+ HSO3-

+ SOl + SOl + SO3" + SOl + 2 IV

+ H +---->SO42" + 2 H + + P

H S O 3 + P A C + H + ~ SO42- + 2 H + + P

SO 2 + 0 3 H20 ) H S O 4 + 02 + H + HSO3" + 03 --) HSO4- + 02 SO3 2- + 03 ----)SO4 2- + 0 2 [Fe(OH)] 2+ + HSO3 --4 Fe 2+ + SO3- + H20 Fe 2+ + SOsH20 ) [Fe(OH)]2+ + H S O f Fe 2+ + H S O f --~ [Fe(OH)] 2+ + SO4-

Fe2, + $2082.

4 . 3 . 107 4 . 6 . 106

H20 ) [Fe(OH)]2÷ + SO42. + I.i+

3.5. 107

n20 S O 5" + SO5" + SOs- +

SO5- + O f

3 . 7 ' 105 1.5" 109 39 4 . 3 . 107

H20 ) Mn3+ + H S O f + OH"

Mn 2+ + S O l Fe 2+ + SO4

3 . 108

2.8.1o 6 4 . 2 . 106 5 . 0 . 105 5 ' I04b 6 . 9 ' 107'[n +] 1.8. 107.[I-1+1 4 . 8 . 107.[H+] 2.4. 104

> [Fe(OH)]2+ + SO42_+ SO4" + H + S O s" "") S2082- + 02 SO5- --->2 SO4" + 02 HO2 -¢' H S O f + 02

H~O ) HSOs- + OH" + 02 SO3" + 0 2 "-~ SOs" SO5 + HSO3" -') HSOs- + S O l SO5- + HSO3" '--'>SO,*2- + SO4" + H + 505- + 5 0 3 2 - - H* -") H S O s + S O 3 S O 5- + SO3 2- ~ S O 4" + SO4 2" O H + HSO4" ---9H20 + SO4S O 4" + S O 4" --~ S2082SO4" + HSO3- -'4 SO42" + SO3" + H + S O 4- + SO32- ~ SO42" + S O 3" SO4- + Fe 2+ -'¢' [Fe(SO,,)]+ SO4" + Mn 2+ .--->SO42- + Mn 3+ SO4" + C u + ---)SO,*2- + Cu 2+ S O 4" + H202 --~ 8042" + H + + HO2 SO4- + MHP --¢ SO42" + n + + CH302 SO4" + HO2 --> SO42- + H + + O~

4000 3800 3990 5530 5280

12 1.8. 108 7 . 2 . 106 1.7. 109 1 . 7 . 109b 2.5. 8.6 3.6 2.1 5.5 3.5 1.6

109 103 102 105 105 l0 s 108

3.2

1o8

3.2 10s 3 . l0 s 2 . 107 3 ' I0 sb

2.8. lO~ 2 . 8 . 1 0 TM 3.5.1o 9

2600 2600

1200

1228

R95 R96 R97 R98 R99 RI00 RI01 RI02

SO4 + O [ ---) SO42 + O2 SO4- + N O [ --->SO42 + NO3 SO4 + OH --~ SO42 + OH SO4 + H20 --->SO42 + H + + OH HSO5 + HSO3 ~+ H ÷ --) 2 SO42- + 3 H ÷ H S O s + SO32 + H + ---) 2 SO42 + 2 H ÷

RI03 RI04 R105 RI06 R107 RI08 R109

CH3OH + O H o2 ~ H20 + HO2 + HCHO CH3OH + SO4 02 ~ SO42 + H + + HO2 + HCHO CH3OH + NO3 _ 0 ~ NO 3 + H ÷ + HO2 + H C H O C H 3 O H + C I 2 O2 ~ 2 C I + H + + H O 2 + H C H O CH3OH + Br2 o2 ~ 2 Br + H + + HOz + H C H O CH3OH+COf o2 ~CO32 + H ÷ + H O 2 + H C H O ETOH + OH ~ HzO + HO2 + CH3CHO ETOH + SO4 ~ SO42 + H + + HO2 + CH3CHO E T O H + N O 3 o2 , N O 3 + H + + H O 2 + C H 3 C H O ETOH + CI2 ~ 2 CI + H ÷ + HO2 + CH3CHO ETOH+Br[ o2 ~ 2 B r + H ÷ + H O 2 + C H 3 C H O ETOH + CO3- o2 ~ CO32 + H ÷ + HO2 + CH3CHO

HSOs + OH ~ SOs + n 2 0 HSO3 + HNO4 ---) SO4 + NO3 + H ÷

3.5. 109b 5 . 0 . lO4

1.4. 107 11 7.14. 106 7.14. 106 1.7. 107 3.1.105

1110

Organic Chemistry

RII0

Rill Rl12 RI13 RII4 RI15 RlI6 RI17 Rl18 Rl19 R120 R121 R122 R123 R124 R125 R126 R|27 R128 R129 R130 R131 R132 R133 R134 R135 RI36 R137 R138 R139 R140 RI41 R142 R143 R144 R145 R146 R147 R148 R149 RI50 R151 R152

CHz(OH)2 + OH ~ H20 + HO2 + HCOOH CH2(OH)2 + SO4 02 ~ SO42 + H + + HO2 + HCOOH CH2(OH)2 + NO3 °2 , NO3 + H + + HO2 + HCOOH C H 2 ( O H h + C I 2 02 ~2C1 + H + + H O 2 + H C O O H CH2(OH)2+Br2 02 ~ 2 B r + H ÷ + H O 2 + H C O O H CH2(OH)2 + CO3 o2 ~ CO32 + H + + HO~ + H C O O H C H 3 C H ( O H ) 2 + O H o2 ~ H 2 0 + H O 2 + H A c CH3CHO + OH rico/o: ) H20 + HO2 + HAc CH3CH(OH)2 + SO4 02 ) 5042 + H ÷ + HO2 + HAc CH3CH(OH)2 + NO3 02 ~ NO3 + H ÷ + HO2 + HAc CH3CH(OH)2 + CI[ - 02 ~ 2 CF + H + + HO2 + HAc CH3CH(OH)z+Br2 02 ~ 2 B r - + H ÷ + H O 2 + H A c CH3CH(OH)2 + CO3 °2 ) CO32 + H+ + HO2 + HAc HCOOH+OH o2 ~ H z O + H O 2 + C O 2 H C O O + OH 02 ~ O H + HO2 + C O 2 H C O O H + S O 4" 02 ~ SO42 + H ÷ + H O 2 + CO2 H C O O + SO4 o2---*S O 4 2- + HO2 + CO2 H C O O H + NO3 - ~ NO3 + H + + HO2 + CO2 H C O O +NO3 02 ~ N O f + H O z + C O 2 HCOOH+CI[ °2 ~ 2 C I + H + + H O 2 + C O 2 HCOO+CI[ °2 , 2 C l - + H O z + C O 2 H C O O H + Brl °2 ~ 2 B r + H ÷ + HO2 + CO2 H C O O + Br2 - ~ - ~ 2 B r + HO2 + CO2 H C O O + CO3 ~ C O 3 2" + HO2 + CO2 HAc + OH -O2-~ H20 + ACO3 + CO2 Ac + O H 02-~OH + A C O 3 + C O 2 HAc+SO4 °2 ~SO42`+H + + A C O 3 + C O 2 A c + SO4 02 , 5042 + CH302 + CO2 HAc + NO3 02 ~ NO3 + H + + ACO3 + CO2 A c + NO3 02 ~ NO3 + CH302 + CO2 HAc+CI2- °2 ~2C1 + H + + A C O 3 + C O 2 Ac- + C12 02 , 2 CI- + CH302 + CO2 H A c + B r 2 - 02 ~ 2 B r + H ÷ + A C O 3 + C O 2 Ac+Br2 o2 ~ 2 B r + C H 3 0 2 + C O 2 Ac- + CO3 02 ) CO32- + CH302 + CO2 CH302 + CH302 ---) CH3OH + H C H O + O2 CH302 + HSO3 ---) MHP + S O l ETHP + ETHP ---) Prod.

1.0. 109 9.0. 106 5.4. 105 1000 5.4.105 2.6. 103 1.9. 109 4.1 • 107 2.2. 106 1.2. 105 3.8. 10 3 1.5" 104 1.0. 109 t . 4 . 107 1.0. 106 3.1.10 4 3 . 10 3b

580 2190 4300 5500

1760 3300

1020 1300 4500 4400

1.3- 104 1.2. 109 3.6. 109 2 . 10 TM 1.9. 106 4 - 104 4" 104b 1 • 104b 1.3. 108 4 , 109 2.5. 106 2.1. 107 3.8. 105 5.1. 107 5500 1.3- 106 4 . 103 4.9. 103 1.4. 105 1.5. 107 1.0. 109 2.0. 105 2 . 8 . 107 1.4. 104 2.9. 106 1950 2.6. 105 10 100 580 1.7. 108 5 . 105 1.5. 108c

1000 1000

3400 2200 4500

3300 1330 1800 1210 3800 3800 4800 4800

2200 -1500

1229

Chlorine chemistry S O 4- + CI" - 4 5 0 4 2 + Cl NO3 + C1- --¢' NO3" + CI C12 + C12"-4 C12 + 2 C1CI2- + Fe 2+ --->2 CI- + Fe 3+ CI2" + Mn 2+ -4 2 CI- + Mn 3+ C12" + Cu + -4 2 CI- + Cu 2+

R153 R154 R155 R156 R157 R158 R159 RI60 RI61 R162

C12" + H202 -4 2 C1- + H+ + HO2 C12- + MHP ---->2 CI" + H+ + CH302 CIf + OH- ~ 2 CI- + OH C12- + HO2 --¢' 2 CI" + H + + 02 C12"+ 02- ~ 2 CI- + O2 C12- + H S O f -4 2 C1- + H + + SO3CI2- + SO32- -4 2 CI" + SO3C12 + H20 -4 H ÷ + CI- + HOCI

R163 R164 R165 RI66

3.3. l0 s

0 4300

1.0. 107 8.7. l 0 s 1.0. 107

3030 4090

8.5. 106 1. 10TM 7.0. 105 7 . 0 ' 105b

3340 3340 b

4.0. 106 1.3- 10 t° 6" 109 1.7. l0 s

400

6.2. 107 0.401

7900

Bromine chemistry SO4- + B r ~ SO42 + Br

R167 R169 RI70 R171 R172 R173 R174 R175 R176 R177 R178 R179

NO3 + Br" ~ NO3" + Br Br2" + Br2" ~ Br2 + 2 BrBrf + Fe 2+ -4 2 Br- + Fe 3+ Br2 + Mn 2+ ~ 2 Br" + Mn 3+ Br2- + Cu + --->2 Br" + Cu 2+

R180 RI81

2.1. 109 3.8- 109 1.7. 109 3.6. 106 6.3. 106 3.6. 106b

3330 4330

1.o. lO5

Br2" + H202 -4 2 Br- + FF + HO2 Br2- + MHP ~ 2 Br- + H + + CH~O2 Br2- + OH" -4 2 B r + OH

1.0. 105b

Br2- + HO2 --> 2 BF + H + + 02 Br2- + 0 2 --~ 2 Br" + 02 Br2- + HSO3- -4 2 Br- + H÷ + SO3Br2 + SO32- --* 2 Br" + SO3Br2 + H20 -4 B r + H+ + HOBr

6.5. 109 1.7. 108 5 . 0 . 107 3.3. 107 1.7

1.1.1o'

780 650 7500

Carbonate chemistry R182 R183 R184 R185

HCO3" + OH -4 H20 + CO3CO32- + OH -4 OH- + CO3 CO32- + S O 4" - 4 SO42" + C O 3" HCO3" + SO4" --~ SO42" + CO3 + H+ CO3 2- + NO3 -4 NO3 + CO¢ CO32- + 0 2 --> 2 C I + CO3 CO32 + Br2- --> 2 Br" + CO3"

R186 R187 R188 R189 RI90 RI91 R192 R193 R194 R195 R196 R197 R198

CO3- + CO3- 02 ) 2 02- + 2 CO2 CO3" + Fe 2+ -4 CO32" + Fe 3+ CO3- + Mn 2+ -4 CO32- + Mn 3+

C O 3- + Cu + -.~ CO32- + Cu 2+ CO3 + H202 -4 HCO3- + HO2 CO3- + MHP --> HCO3- + CH302 CO3- + HO2 -4 HCO3 + 02 C O 3" + 0 2- - 4 CO3 2" + 0 2 CO3 + HSO3- -4 HCO3" + SO3 C O 3" + 5032- - 4 CO32" + S O 3"

1900 2550

1.7. 107 109 4.1. 10 TM 1 •

2090

2.8. 106 1.7- 10 TM 2.7- 106b 1.1. 105 2.2- 106 2 . 10 TM 1 . 5 ' 107 2 . 10TM 4.3. 105 4.3. 105b

6.5" l 0 8b 6.5-10 8 1 • 1 0 TM

470

5 . 0 ' 106

Table 5: Photolysis Rates Reaction No. P1 P2 P3 P4 P5 P6

Reaction

J [s"l]

14202 + hv--.> 2 OH [Fe(OH)]2++ hv --~ Fe 2+ + OH

7.19. 10,6 4.51 . 10-3 5.77- 10.3 6.43. 10.3 2.57.10 .5 4.28- 10 .7

[Fe(OH) 2]÷ + hv -4 Fe 2+ + OH + O H [Fe(SO4)I ÷ + hv ~ Fe 2÷ + SO4NO2- + hv n+ ) NO + OH NO3-+ hv n+ ~.NO2 + OH

1230 T a b l e 6: A d d i t i o n a l h a l o g e n a c t i v a t i o n e q u i l i b r i a a n d r e a c t i o n s Reaction No.

Equilibrium~

E31 E32 E33 E34 E35 E36 E37 E38 E39 E40 E41

HOBr ~ H ÷ + OBrHOC1 .,.._.a H ÷ + OCI HBrO2 ~ H ÷ + BrO2 BrCI ~ HOBr + C l + H + BrCI ~ HOCI + B r + H + Br2CI- ~ BrCI + BrBrCI2 ~ BrC1 + CI Br2CI ~ Br2 + CI BrCI2 "--"" C12 + Br BrCI w'--" B r + CI BrCI- - - " " C I + Br

Reaction No. R199 R200 R201 R202 R203 R204 R205 R206 R207 R208 R209 R210

3

k 298, M n Sd

Ea/R,

k 298,

M" s -1 5.101° 5.10 I° 5.10 I°

K

105 1600 105 11

E,/R, K

1

2500 7.7.109 7.7.109 7.7.109 7.7.109 2.10 I° 2.10 I°

1

4.3.105 1.3.1o 9

5.9.109 5.9-109 8.10 4 8.10'

k298, M n sd

Aqueous Phase Reactions

Ej/R, K

1.3.1o 7

H ÷ + CI- + HOCI -~ C12 + H20 H + + Br + HOBr --~ Br2 + H20 BrO + BrO --) BrO2- + OBr- + 2 H ÷ BrO2- + BrO --~ OBr + BrO2 HO2 + HOBr --) H20 + 02 + Br 0 2 + HOBr --) OH- + 02 + Br HO2 + Br2 --~ Br2 + 02 + H + HO2 + Br2 -4 Br2 + 02 HO2 + HOCI ~ H20 + 02 + CI O2 + HOC1 ---)OH- + O2 + CI HO2 + C]2 -"> CI2 + 02 + H + HO2 + C12 -~ C12 + 02

1.6.10 l° 2,8.109 4.10 s 1.109 3.5.109 1.1.10 s 5.6.109 7.5.106 7,5.106 1.109 1.109

Results

In F i g u r e

1 the o b t a i n e d a q u e o u s p h a s e c o n c e n t r a t i o n l e v e l s for OH- a n d NO3. are s h o w n for u r b a n

conditions.

2.0

~l,,,i,i

,I,,,

i~ . . . . -NO~ .... OH

•'

1.8 ,'

1.6 ~

~

, 1.4

o

,

1.2 1.0

- -

~,-,~ 0.8 ,

0.6

o

0.4 ~ ,' ~.-~ . . . . 6

F i ~ d r e 1: C A P R A M :

i .....

~.~

12

18

24 6 Time of day / h

12

18

24

C o m p a r i s o n o f m o d e l l i n g r e s u l t s for [OH]aq a n d [NO3]aq u n d e r u r b a n c o n d i t i o n s .

1231 During day time the concentration of the .OH radical reaches about 2.10"12 M. The NOT radical is formed at night-time, but its maximum concentration is nearly one order of magnitude smaller than the .OH-radical at daytime. Nearly 50 % of the .OH radical in the aqueous phase is transferred from the gas phase. The other half is produced in the reactions of H202 with Fe2÷ and Cu÷. The main sinks of the .OH radical are established through oxidation reactions of organic species, such as CH2(OH)2, HCOOH/HCOO and CH3OH. The importance of the OH radical is due to its efficiency in the oxidation of the organic compounds. Diagnosis performed show that the oxidation by OH is the main reaction pathway, through which the oxidation chain from the alcohols to the aldehydes and at last to the carbonic acids is established. Comparisons between the three investigated scenarios show that the OH concentration in the marine scenario is highest. This effect can be explained with the lower initial concentrations of organic species in the marine case. The NO3. radical is at night time exclusively transferred from the gas phase. The mass fluxes from the other source reaction, i.e. the oxidation of nitrate by the sulphate radical anion, is negligible. Quite different from the hydroxyl radical, NO3. mainly reacts with chloride and bromide. Although the rate of the reaction with bromide is nearly two orders faster, the reaction with chloride dominates, because the concentration is nearly a factor 300 higher. In the urban scenario most NO3. is predicted, because its main source reaction in the gas phase is the oxidation of NO2-, the initial concentration of which under polluted conditions is a factor 15000 higher compared to the marine scenario. These results mentioned so far were obtained with CAPRAM without extension. In order to describe the marine chemistry in more detail, the chemical reactions listed in Table 6 were added to CAPRAM. This extended mechanism was compared with the aqueous phase mechanism by Sander and Crutzen [8]. In a first step only the reactions between the halogen containing species in the gas phase with ozone and HO2. were added to the HOX halogen activation mechanisms. It is observed that nearly 10 orders of magnitude more chlorine atoms are produced from CAPRAM (101° cm3 after the first day). Also the concentration level of the bromine atom is nearly two orders higher. At the second day of calculations ozone has a maximum concentration of nearly 108 cm 3, while it is reduced by the mechanism after Sander and Crutzen from 2.2.1012 cm "3 only to 1.8-1012 cm 3. In further calculations in both mechanisms the reaction between methane and the chlorine atom were implemented. The corresponding reaction with bromine was neglected, because of the very small reaction rate constant. This comparison leads to similar concentration levels for O3. The level of the bromine atom produced by CAPRAM in this case is even nearly three orders of magnitude lower (1 cm3) than obtained with the mechanism by Sander and Crutzen. Also the concentration of the chlorine atom is reduced in both mechanisms(CAPRAM 1 cm-3, mechanism by Sander 10-6 cm3), because this species has an important sink in the reaction with methane. This effect can be explained with a reaction chain, that causes a ozone production in the presence of chlorine atoms: The reaction of methane and chlorine atoms in the presence of 02 leads to the methylperoxy radical. RADM2 contains the further reactions of this species with NO- to NO2. and formaldehyde. NOr is photolysed to NO. and O.(3P), which is immediately converted to ozone. A comparison of the concentration levels of the methylperoxyl radical between the CAPRAM model runs with and without consideration of the chlorine atom reaction with methane shows that the added reaction causes a increase of the concentration of the methylperoxyl radical from 4.107 to 9.10s cm-3 at noon. The loss fluxes of ozone in the reactions with the halogen atoms are similar in the mechanism of Sander and Crutzen when compared to CAPRAM. Therefore, altogether in CAPRAM more ozone is destructed by the halogen atoms, but this effect is compensated by an increased

1232 formation of methylperoxyl radicals and hence ozone, so that the resulting ozone concentration is comparable to the one found in the mechanism by Sander and Crutzen. The increased chlorine atom production in CAPRAM is due to the fact that in the mechanism formulated by Sander and Crutzen the recombination of C12. radical anions is not included, so that less C12 is produced in the aqueous phase and hence less gas phase chlorine atoms are formed. In both mechanisms the reaction between the chlorine atom and methane is the most important sink because of the high gas phase concentration of methane. 4 Conclusion With the calculations performed using CAPRAM the concentration levels of several radicals are determined. The most important radicals in the tropospheric aqueous phase are the .OH radical during daytime and the NO3. radical at night-time. The maximum concentration of the .OH at noon is nearly 2.10 -12 M. The main source is transfer from the gas phase and in-situ generation by Fenton-type processes..OH loss mainly occur by organic species such as formic acid and formaldehyde. At night-time NOy reaches concentrations of 2-10a3 M. Its only source is transfer from the gas phase. The sinks of this species are the reactions with chloride and bromide. The halogen activation mechanism added to CAPRAM produces nearly 101° cm 3 chlorine atoms and 105 cm 3

bromine atoms during one day while in the aqueous phase mechanism

formulated by Sander and Crutzen these values are ten orders respectively three orders of magnitude smaller. Because of this the ozone in the gas phase in CAPRAM is negligible after few hours; the ozone concentration in the Sander mechanism is only reduced by less than 10% after three days of calculation. If the reaction of methane and the chlorine atom in the gas phase is added to both mechanisms the concentration levels of ozone in CAPRAM is equal (1.8.1012 cm -3) to the other mechanism. This effect is due to an increased C1. production caused by formation of C12 and HOCI in the aqueous phase in CAPRAM because of the recombination of the dichloride radical anion (C12-.). After the transfer to the gas phase and photolysis to chlorine atoms, the C1. atoms do not only destruct ozone by C10. formation, but also produce ozone indirectly via the increased formation of CH302.. 5 Acknowledgements Part of the present study has been performed within the project "Model Development for Atmospheric Aqueous Phase Chemistry (MODAC)" which is supported by the European Commission under contract ENV4-CT97-0388. The authors acknowledge early efforts of H.-W. Jacobi in mechanism testing. 6 References [1] Stockwell, W. R., Middleton, P., Chang, J. S. and Tang, X., J.Geophys.Res. 95, 16343 - 16367 (1990). [2] Jacob, D. J., J.Geophys.Res. 91, 9807 - 9826 (1986). [3] Lelieveld, J. and Crutzen, P. J., J.Atmos.Chem. 12, 229 - :268 (1991). [4] Walcek, C., Yuan, H. H. and Stockwell, W. R.,Atmos. Env. 31, 8, 1221-1237 (1997). [5] M~ller, D. and Mauersberger, G., J. Atmos. Chem. 14, 153-1651 (1992). [6] Vogt, R., Crutzen, P. J., Sander, R., Nature, 383, 327 (1996). [7] Graedel, T. E. and Keene, W. C., Global Biogeochem. Cyc. 9, 47-77 (1995). [8] Sander, R. and Crutzen, P. J., J.Geophys.Res. 101, 9121 - 9138 (1996). [9] Schwartz, S. E., Mass transport considerations pertinent to aqueous phase reactions of gases in liquidwater clouds, in: W. Jaeschke, Chemistry of Multiphase Atmospheric Systems, NATO ASI Series, 1991, [10] Herrmann, H., Ervens, B., Jacobi, H.-W., Wolke, R. and Zellner, R., submitted to J. Atm. Chem. (1998).